The Directory For Masses With Children (DMC) allows for a separate Liturgy of the Word for children, however, the directory is clear that the children should return to the adults before the Eucharistic Liturgy begins: “Sometimes, moreover, if the place itself and the nature of the community permit, it will be appropriate to celebrate the Liturgy of the Word, including a homily, with the children in a separate, but not too distant, room. Then, before the Eucharistic Liturgy begins, the children are led to the place where the adults have meanwhile celebrated their own Liturgy of the Word” (DMC 17).
Concerning the children’s Sunday obligation, canon law obliges Catholic children to participate in the Sunday Mass once they possess the use of reason and have completed seven years of age. Participating in a Mass utilizing the children’s Liturgy of the Word satisfies this obligation. Although illicit to return the children late, such children still fulfill their obligation because (1) there is no strict rule on how much or what portion of the Mass must be attended to satisfy one’s obligation, and (2) the children are not at fault.